Northwest Michigan fruit update – July 21, 2020
Cherry harvest is in full swing northwest Michigan. Growers are harvesting both sweet and tart cherries at this time.
The weather has cooled down after what seemed like a long stretch of hot days earlier in the season. The cooler weather is a blessing as we are in the full throes of cherry harvest. Daytime temperatures have been in 70s to low 80s, and we have even seen nighttime temperatures in the 50s last night. Cool weather is in the forecast until the weekend, when temperatures might be in the 90s again.
We have accumulated 1,850 growing degree days (GDD) base 42 and 1,214 GDD base 50. Surprisingly, we have moved ahead of our long-term averages: 1,816 GDD base 42 and 1,105 GDD base 50.
We also had some significant rainfall throughout the region. Again, as has been typical of 2020, the rainfall was variable across the different parts of the five-county area. At the Northwest Michigan Horticulture Research Center, the Michigan State University Enviroweather station recorded 0.75 inches of rain on July 15. We also had substantial rainfall over the weekend on both Saturday and Sunday where we received 1.19 inches on July 19 and 0.7 inches of rain at the Northwest Michigan Horticulture Research Center. The rain came really fast, and some growers reported much more rain than what was recorded at the Northwest Michigan Horticulture Research Center Enviroweather station.
Both sweet and tart cherry harvest are underway across the region. In most years, sweet cherries ripen earlier than tart cherries, but the sizes of the crops and the recent hot weather has ripened both crops at a similar time. There is less cracking in sweet cherries than expected with the weekend’s rains. Lighter sweet cherries have more cracks than canner varieties. Tart cherry quality is excellent.
Spotted wing Drosophila update
We have seen a considerable upswing of spotted wing Drosophila (SWD) trap catch over the past week. The weather has been favorable for this increase with cooler temperatures, rainfall and higher humidity. The crops are also at a susceptible stage, which is also likely influencing the activity of the flies. We checked some traps throughout the five-county area on July 20 and found that some traps are catching one and two flies per trap, but many traps are catching double digits, such as 13, 10 and 27 flies in three traps in Leelanau County. We expect these numbers to continue to rise in the coming days, and growers will need to protect their crop from infestation.
We have also been collecting tart cherry fruit in an unsprayed block at the Northwest Michigan Horticulture Research Center to look for larvae. Each day, we collect 150 fruit from each of five areas in an unsprayed block of 18-year-old tart cherries. On July 20, we found larvae in all but two of the samples. The number of larvae in these samples ranged from one to 15 larvae. These larval numbers indicate that the flies are present in the orchard, and they are actively laying eggs in fruit.
We have also been collecting fruit from grower farms to examine them for larvae. We have found larvae in fruit in blocks that have been managed for SWD. This finding is alarming, particularly as the number of flies has been low until recently. There does not seem to be much correlation between the number of flies in the traps and the potential to have larvae in fruit. Regardless, trap counts are rising and will likely continue to rise, and growers need to be actively managing for SWD at this critical time. Both sweet and tart cherries are vulnerable to SWD oviposition, and growers need to be sure to be covered during this harvest period.
Rain is in the forecast and retreatment will be needed if areas receive rainfall that washes off sufficient residue to protect fruit. For most products, 0.5 inches or more of rain warrants retreatment to ensure fruit are protected from SWD. We do have a three-day preharvest interval for Mustang Max in both sweet and tart cherries, which may be a good tool for growers during this harvest timing. Keep in mind that there are a few restrictions on these special labels including a seven-day retreatment interval and no more than 24 fluid ounces of product per acre per year can be applied.